Dan Johnson

What is a hashing function? Fingerprint for a given piece of data Typically generated by a mathematical algorithm Produces a fixed length string as its output Hashes are sometimes called a checksum or message digests

Cryptographic hashing functions Have four major properties: It is impossible for any given output to determine the original input. This does not mean we can’t use inference to find input that is likely correct It is easy to compute the hash of any given input. Easy means that it does not require a lot of system resources or time to compute the hash of a given input.

(cont…) It is infeasible to determine two inputs that produce the same output. It is infeasible to change an input and produce the same output. Infeasible means that a solution cannot be found in less time than by brute force.

Cryptographic Strength Determined by output length and ability to resist cryptanalytic attack Output length expressed in number of bits Attacks attempt to break one of the cryptographic properties.

Preimage Attacks Two types, “first-preimage” and “second-preimage” Both attempt to break the one way property of the hashing function Both are similar in nature If a hashing function is vulnerable to one form of preimage attack, it is likely vulnerable to the other form of attack Successful attack executes in less that brute force time

Collision Attack A collision occurs when two pieces of input produce the same output. Collision attacks take advantage of a property of probability theory called the birthday paradox or birthday problem. Collision attacks attempt to find a collision in less than O(2 n/2 )

MD5 Published by Ronald Rivest in Produces 128-bit output, represented by 32bit hexadecimal number. Vulnerable to collision attacks. Now mostly used for creating checksums of large files.

SHA-1 Created by the National Security Agency Creates a 160-bit message digest represented by a 20 character string More secure than MD5 Widely popular and used in many applications In 2005, a group of Chinese researches discovered mathematical errors that could lead to a preimage attack in less than brute force time. No known attacks based on these findings have surfaced.

SHA-256 Also created by NSA as a part of the SHA2 family which includes SHA224, SHA256 and SHA512. Creates a 256bit output, hence its name. Considered to be more secure than SHA1 because of increased bit size. Mathematical problems found in SHA1 are not present in SHA256. Less popular than SHA1.

Hash Based Authentication Works the same way as password authentication Store hashed value of password in database instead of password itself When a user attempts to authenticate, hashes input value and compares it with value stored in database “password” => [ ﾪ aä ɹ ?? ﾂ %lø3~æ ﾏ Ø

Example implementation Consider the following PHP code snippet. From this we can clearly see that adding hash based authentication does not add a much code.

What an attacker sees… Without encryption: With just SHA-1 encryption: UsernamePassword Nigelpenguin Alfredpenguin UsernamePassword Nigels3\"¹\?óðt½ž…PèÔŽ Alfreds3\"¹\?óðt½ž…PèÔŽ

Cont… Can this be improved? Better solution: sha1( username + password) Even better solution: sha1( sha1(username) + sha1(password) ) UsernamePassword NigeläQÞË‚HBŽ{<7r‚¿i}_H ›\eV€J×ÜÇ UsernamePassword NigeläQÞË‚HBŽ{<7r‚¿i}_H ›\eV€J×ÜÇ

Microsoft Store India Earlier this year, the Microsoft Store web site for India was breached. Attackers stole hundreds of thousands of usernames and passwords. All passwords were stored in plaintext. Credit Card information was also not encrypted in any from. Many users had their identity compromised and fraudulent purchases charged to their credit card.

Sony Playstation Network and Sony Pictures customer databases were both breached in Credit card information was encrypted, but several reports indicate that encryption may have been compromised. User data was not encrypted in any way. Class action lawsuit filed over negligence.

Other protection methods Hashing not good for everything. Credit card information could be stored using symmetric key encryption. This allows for the input to be determined at a later date. BE SUPER CAREFUL!

Questions?

References Agarwal, A. (2012, February 27). Not just addresses, credit card numbers also stolen from microsoft india store. Retrieved from store-hacked/20891/ Gallagher, S. (2012, February 14). Microsoft's store site in india defaced; hackers find plain text passwords. Retrieved from hackers-find-plain-text-passwords.ars McGlinn, J. (2005, March 20). Password hashing. Retrieved from Silva, J. (2003). An overview of cryptographic hash functions and their uses. Retrieved from hash-functions_879 Schneier, B., & Hoffman, P. (2005). attacks on cryptographic hashes in internet protocols. Retrieved from Schwartz, M. (2011, June 3). Sony hacked again, 1 million passwords exposed. Retrieved from Stallings, W., Brown, L., & Howard, M. (2008). Computer security, principles and practice. Upper Sadddle River, NJ: Pearson Education. Ullrich, J. (2011, June 28). Hashing passwords. Retrieved from